In general, analysis apparatus, such as spectroscopic analysis apparatus are used to investigate the composition of an object to be examined. In particular analysis apparatus employ an analysis, such as a spectroscopic decomposition, based on interaction of the matter of the object with incident electromagnetic radiation, such as visible light, infrared or ultraviolet radiation.
The invention relates to an analysis apparatus, in particular a spectroscopic analysis apparatus, comprising
an excitation system (exs) for emitting an excitation beam (exb) to excite a target region during an excitation period
a monitoring system (lso) for emitting a monitoring beam (irb) to image the target region during a monitoring period.
Such an analysis apparatus is known from the U.S. Pat. No. 6,069,690.
The known analysis apparatus concerns a dual mode integrated laser imaging and spectral analysis system, which is used to view and analyse defects on a work piece such as a semiconductor wafer. This known analysis apparatus has two operating modes, namely a scanned imaging mode and a stop scan spectral analysis mode. During the scanned imaging mode the monitoring beam in the form of a laser beam is emitted and the target region is imaged. Separately from the imaging, in the stop scan mode, the laser beam is employed for excitation and spectral analysis can be carried out. However, the known analysis apparatus is suitable only for analysis of a stationary object.
An object of the invention is to provide an analysis apparatus that enables accurate analysis of a spatially moving target region.
This object is achieved by an analysis apparatus according to the invention wherein the monitoring period and the excitation period are substantially overlapping and the analysis apparatus is provided with a tracking system (osc, dcu) to control the excitation system to direct the excitation beam onto the target region.
The analysis apparatus of the invention is provided with the tracking system which controls the excitation system notably so as to keep the excitation beam directed to the target region if the target region moves. The tracking system in particular maintains focussing of the excitation beam on the target region. Hence, the excitation of the target region continues while the target region moves and also scattered radiation is being generated by the excitation beam. Thus, the analysis apparatus of the invention can follow a moving detail while continuing the spectroscopic analysis. Hence, the acquisition of spectroscopic data can be integrated in time, even when an appreciable movement of the detail at issue occurs. The signal-to-noise ratio of the spectroscopic data is accordingly increased by the integration. The analysis apparatus of the invention is in particular suitable to perform in vivo Raman spectral analysis of blood in a bloodvessel in the patient""s skin. The patient""s pulsating blood flow or the patient""s muscle movements cause movements of the blood vessels and consequently in the image formed by the monitoring beam the rendition of the bloodvessels move. Especially, appreciable movement can occur of capillary vessels underneath the surface of the patient""s skin.
Preferably, the tracking system also controls the monitoring system, notably the tracking system controls focussing of the monitoring beam on the target region. During the overlap of the excitation period and the monitoring period, the excitation of the target region and the monitoring of the target region occur simultaneously and/or alternatingly. Because the target region is imaged together with the excitation, an image is formed displaying both the target region and the excitation area. On the basis of this image the excitation beam can be very accurately aimed at the target region. Consequently, the excitation beam generates scattered radiation almost exclusively in the target region, as at least the target region is included or partly included, in the area that is excited by the excitation beam. The scattered radiation from the target region is detected and the composition of the target region is derived from the scattered radiation. Because the monitoring beam is continuously focused on the spatially moving target region, imaging of the target region and consequently its monitoring is continued even for a moving target, such as a capillary bloodvessel underneath the surface of the skin.
Directing the excitation beam and/or the monitoring beam involves control of the spatial orientation of these beams and also control of the position where these beams are focused. As elaborated with reference to the detailed embodiments, various optical arrangements are suitable to perform such control.
More preferably, both the monitoring beam and the excitation beam are controlled to be directed onto the target region by the tracking system. In this preferred embodiment the monitoring beam is kept directed onto the target region which is then being imaged while the target region moves and meanwhile the target region is being excited by the excitation beam.
In a preferred embodiment of the analysis apparatus of the invention the motion detection system determines the movement of the target region and produces the error signal which represents the motion. The error signal is applied to the tracking system and on the basis of the error signal the tracking system controls the excitation system and/or the monitoring system.
There are various embodiments of the motion detection system. For example, the motion detection system is arranged to receive a series of successive images of the target region. These images preferably also include some of the surroundings of the target region. The images are conveniently supplied by the monitoring system which images the target region by way of the monitoring beam. From the successive images the motion detection system derives the movement of the target. To this end image processing algorithms can be employed which automatically detect the target region from its particular shape and/or its brightness in the successive images being distinct from its surroundings in the images.
In another example the motion detection system receives scattered radiation generated by the excitation beam. In many applications, notably such as Raman spectroscopy of capillary bloodvessels, the intensity or spectral shape of scattered radiation is substantially different from the target region relative to its surroundings. In particular, Raman scattering in pre-selected wavenumber regions from the bloodvessel in the target region is markedly different as compared to Raman scattering from the skin tissue next to the bloodvessel. In this embodiment of the analysis apparatus the motion detection system derives the error signal from the intensity of the (notably Raman) scattered radiation. Especially, the motion detection system is arranged to make successive comparisons of the intensity of the scattered radiation to a reference value to obtain the error signal. The error signal is then used as a feedback to the tracking system to control the excitation beam and/or the monitoring beam so as to maintain a constant value of the error signal level or keep the signal level of the error signal within predetermined limits, and consequently maintain the intensity of the scattered radiation at a stable level which causes especially the excitation beam to remain being directed onto the target region.
In a further preferred embodiment the analysis apparatus of the invention is provided with a depth setting system to control the focus depth of the monitoring beam and/or the excitation beam. As will be elaborated with respect to the detailed embodiments, various optical arrangements can be employed to control the focus depth of these beams. In a preferred embodiment the depth setting system is arranged to vary the angle of incidence of the monitoring beam on the target region. As a consequence, an object in the focus of the monitoring beam is stationary in the image formed by the monitoring system whereas any images of an object outside of the focus of the monitoring beam is subject to apparent motion owing to parallax. When the target is imaged, its depth is determined on the basis of imaging from various orientations and its apparent motion is observed. Then the excitation beam is focussed at exactly the depth of the target region. Controlling the focus depth of the monitoring and/or the excitation beam is especially advantageous in the application of the analysis apparatus of the invention to Raman spectroscopy of a bloodvessels underneath the skin surface of the patient""s skin.
The invention also relates to a method of spectral non-invasive analysis of an object. The method according to the invention is defined in Claim 9. This method is in particular advantageous for spectral non-invasive analysis of blood in vivo.
These and other aspects of the invention will be further elaborated with reference to the embodiments defined in the dependent Claims.